JPH07216524A - Hot dipping method of high tensile strength hot rolled steel plate - Google Patents
Hot dipping method of high tensile strength hot rolled steel plateInfo
- Publication number
- JPH07216524A JPH07216524A JP656494A JP656494A JPH07216524A JP H07216524 A JPH07216524 A JP H07216524A JP 656494 A JP656494 A JP 656494A JP 656494 A JP656494 A JP 656494A JP H07216524 A JPH07216524 A JP H07216524A
- Authority
- JP
- Japan
- Prior art keywords
- hot
- plating
- rolled steel
- steel sheet
- oxide film
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、めっき欠陥を発生させ
ることなく、高張力熱延鋼板を連続的に溶融めっきする
方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously hot-diping a high-strength hot-rolled steel sheet without causing plating defects.
【０００２】[0002]
【従来の技術】高張力熱延鋼板は、車両用構造部材，建
材，機械部品等の広範な分野で使用されている。耐食性
を向上させた鋼板として、ゼンジマー法等によって溶融
亜鉛めっきした高張力熱延鋼板も使用されている。高張
力熱延鋼板を溶融めっきする際、低温加熱還元工程での
還元不足に起因して不めっきが生じ易く、製品歩留りを
低下させる原因となっている。不めっきは、Ｆｅ，Ｎ
ｉ，Ｚｎ等のプレめっきにより防止される。しかし、プ
レめっきは、工数の増加，工程管理，操業安定性等に問
題がある。そこで、プレめっきを必要とすることなく、
良好な溶融めっきを高張力熱延鋼板に施すことが従来か
ら検討されている。たとえば、特開平３−６１３５２号
公報では、脱スケールされた熱延鋼板の表面層を僅かに
研削した後、鋼板強度を損なわない範囲での低温加熱に
よって表面改質している。また、特開昭４９−１３０３
７号公報では、熱延鋼板のスケールを機械的に除去した
後、還元加熱を経てめっきしている。また、脱スケール
後、必要に応じて酸化処理し、還元加熱を経てめっきす
る場合もある。2. Description of the Related Art High-strength hot-rolled steel sheets are used in a wide range of fields such as vehicle structural members, building materials, and machine parts. As a steel sheet with improved corrosion resistance, a high-strength hot-rolled steel sheet hot-dip galvanized by the Zenzimer method or the like is also used. When hot-rolling a high-strength hot-rolled steel sheet, non-plating is likely to occur due to insufficient reduction in the low-temperature heat reduction step, which is a cause of lowering the product yield. Non-plating is Fe, N
It is prevented by pre-plating with i, Zn or the like. However, the pre-plating has problems in increase of man-hours, process control, operational stability, and the like. So without the need for pre-plating,
It has been studied so far to apply good hot dip coating to high-strength hot-rolled steel sheets. For example, in Japanese Patent Laid-Open No. 3-61352, the surface layer of a descaled hot-rolled steel sheet is slightly ground and then surface-modified by low-temperature heating within a range that does not impair the strength of the steel sheet. Also, JP-A-49-1303
In Japanese Patent Publication No. 7, the scale of the hot rolled steel sheet is mechanically removed, and then reduction heating is performed for plating. In addition, after descaling, an oxidation treatment may be carried out if necessary, and a plating may be carried out after reduction heating.
【０００３】[0003]
【発明が解決しようとする課題】高張力熱延鋼板を溶融
めっきしたとき良好なめっき層が形成されない原因の一
つに、強度向上元素として添加されているＳｉ，Ｍｎ等
の影響がある。表面研削後に低温加熱する特開平３−６
１３５２号公報の方法では、表面研削によって鋼板表面
が一旦清浄化されるものの、予熱炉や還元炉での加熱時
に易酸化性元素であるＳｉ，Ｍｎ等が選択酸化され、酸
化物として鋼板表面に濃縮する。濃縮したＳｉ，Ｍｎ等
は、めっき金属に対する鋼板表面の濡れ性を低下させ、
めっき性を阻害する。他方、研削ブラシ等を使用して鋼
板表面のスケールを機械的に除去する特開昭４９−１３
０３７号公報の方法では、酸洗のような均一処理が難し
く、部分的にスケールが残存し易い。たとえば、コイル
形状が悪い場合、部分的にブラシが当らないところがあ
り、またコイルによって板幅が異なることからブラシが
不均一に劣化する。その結果、脱スケーリングされた鋼
板表面にムラが生じる。One of the reasons why a good plating layer is not formed when hot-rolling a high-strength hot-rolled steel sheet is affected by Si, Mn, etc. added as a strength improving element. Heating at low temperature after surface grinding
According to the method disclosed in Japanese Patent No. 1352, the surface of the steel sheet is once cleaned by surface grinding, but Si, Mn and the like which are easily oxidizable elements are selectively oxidized at the time of heating in a preheating furnace or a reduction furnace, and the surface of the steel sheet is oxidized as an oxide. Concentrate. Concentrated Si, Mn, etc. reduce the wettability of the steel plate surface with respect to the plating metal,
Inhibits platability. On the other hand, the scale on the surface of the steel sheet is mechanically removed using a grinding brush or the like.
In the method of 037, uniform treatment such as pickling is difficult, and the scale easily remains partially. For example, if the shape of the coil is not good, the brush may not come into contact with the part, and the plate width varies depending on the coil, so that the brush deteriorates unevenly. As a result, unevenness occurs on the surface of the descaled steel sheet.
【０００４】また、Ｓｉ含有鋼板等にあっては、緻密な
内部酸化スケールが発生している。この種の内部酸化ス
ケールは、研削ブラシ等で極めて除去し難く、機械的な
脱スケーリングの適用を一層困難にする。そのため、ス
ケールを完全に除去しようとすると、通板速度を低下せ
ざるを得ず、生産性が悪くなる。すなわち、従来法で処
理された鋼板表面には、依然としてスケールが部分的に
残存している。残存スケールは、還元加熱で除去可能な
厚みを超えており、不めっき発生の原因となる。本発明
は、このような問題を解消すべく案出されたものであ
り、ガス還元に先立って熱延鋼板を脱スマット処理及び
弱酸化することにより、Ｓｉ及びＭｎの拡散を抑制する
作用を呈する薄いＦｅの酸化皮膜を鋼板表面に均一に形
成し、溶融めっきに適した表面状態に熱延鋼板を改質
し、めっき欠陥のない溶融めっきを施すことを目的とす
る。In addition, in a Si-containing steel plate or the like, a dense internal oxide scale is generated. This type of internal oxide scale is extremely difficult to remove with a grinding brush or the like, making it more difficult to apply mechanical descaling. Therefore, if the scale is to be completely removed, the strip passing speed must be reduced, and the productivity is deteriorated. That is, the scale still partially remains on the surface of the steel sheet treated by the conventional method. The residual scale exceeds the thickness that can be removed by reduction heating, and causes non-plating. The present invention has been devised to solve such a problem, and exhibits an action of suppressing diffusion of Si and Mn by desmutting and weakly oxidizing a hot-rolled steel sheet prior to gas reduction. An object is to uniformly form a thin Fe oxide film on the surface of a steel sheet, modify the hot-rolled steel sheet to a surface state suitable for hot dip coating, and perform hot dip plating without plating defects.
【０００５】[0005]
【課題を解決するための手段】本発明の溶融めっき方法
は、その目的を達成するため、強化元素としてＳｉ及び
Ｍｎを含む高張力熱延鋼板を脱スケール酸洗後に脱スマ
ット処理し、弱酸化性雰囲気中で加熱して鋼板表面に５
００〜１００００Åの膜厚を持つＦｅの酸化皮膜を形成
した後、水素濃度３〜２５容量％の雰囲気に保持された
還元炉で還元加熱し、次いで溶融めっきすることを特徴
とする。鋼材の強度を高める添加元素としては、Ｃ，Ｓ
ｉ，Ｍｎ，Ｐ等があり、材質の要求レベルに応じた成分
設計が採用される。代表的な成分系としては、Ｃ−Ｓｉ
−Ｍｎ系，Ｃ−Ｍｎ系，Ｃ−Ｍｎ−Ｐ系等がある。Ｃ含
有量が大きいほど強度が高くなるが、０．３重量％を超
えるＣ含有量では溶接性が著しく劣化する。そこで、Ｃ
含有量は、通常０．００１〜０．３重量％の範囲にす
る。Ｓｉは、含有量が２．０重量％を超えると熱間圧延
時に厚い内部酸化スケールを生成させ、脱スケール酸洗
性の劣化や表面外観の不均一性の原因となるため、通常
０．００１〜２．０重量％の範囲にする。ここで、Ｓｉ
無添加の高張力鋼も本発明の対象としていることから、
Ｓｉ含有量の下限を０．００１重量％にしている。しか
し、Ｓｉ添加によって強度向上を図る場合、０．２重量
％以上のＳｉを含有させることが一般的である。Ｍｎ
は、強度及び靭性を向上させる作用があるため、現在で
は高張力鋼を設計する際の必須元素となっている。強度
の面から、０．４重量％以上のＭｎ含有量が必要であ
る。しかし、Ｍｎ含有量が３．０重量％を超えると、鋼
材が過度に硬質化し、加工性が劣化する。したがって、
Ｍｎ含有量は、通常０．４〜３．０重量％の範囲に定め
る。Ｐは、強度の向上に有効であるが、０．１５重量％
を超える含有量では脆化，溶接性の劣化等の悪影響が現
れる。そのため、Ｐ含有量は、通常０．００１〜０．１
５重量％の範囲にする。ここで、Ｐ無添加の高張力鋼も
本発明の対象としていることから、Ｐ含有量の下限を
０．００１重量％にしている。しかし、Ｐ添加で強度向
上を図る場合、０．０４重量％以上のＰを含有させるこ
とが一般的である。[Means for Solving the Problems] In order to achieve the object, the hot-dip galvanizing method of the present invention performs high-strength hot-rolled steel sheet containing Si and Mn as strengthening elements by descaling, desmutting treatment, and weak oxidation. On the steel plate surface by heating in a strong atmosphere
After forming an Fe oxide film having a film thickness of 00 to 10000Å, it is subjected to reduction heating in a reducing furnace kept in an atmosphere having a hydrogen concentration of 3 to 25% by volume, and then hot dip plating. As additive elements for increasing the strength of steel materials, C, S
i, Mn, P, etc., and the component design according to the required level of the material is adopted. A typical component system is C-Si.
There are -Mn type, C-Mn type, C-Mn-P type and the like. The higher the C content, the higher the strength, but if the C content exceeds 0.3% by weight, the weldability deteriorates significantly. So C
The content is usually in the range of 0.001 to 0.3% by weight. When Si content exceeds 2.0% by weight, thick internal oxide scale is generated during hot rolling, which causes deterioration of descaling pickling property and non-uniformity of surface appearance. To 2.0% by weight. Where Si
Since high-strength steel without additives is also the subject of the present invention,
The lower limit of the Si content is 0.001% by weight. However, in order to improve the strength by adding Si, it is common to contain 0.2% by weight or more of Si. Mn
Has an effect of improving strength and toughness, and is now an essential element when designing high-strength steel. From the viewpoint of strength, a Mn content of 0.4% by weight or more is required. However, when the Mn content exceeds 3.0% by weight, the steel material is excessively hardened and the workability deteriorates. Therefore,
The Mn content is usually set in the range of 0.4 to 3.0% by weight. P is effective for improving strength, but 0.15% by weight
If the content exceeds the range, adverse effects such as embrittlement and deterioration of weldability appear. Therefore, the P content is usually 0.001 to 0.1.
The range is 5% by weight. Here, since the high-strength steel containing no P is also an object of the present invention, the lower limit of the P content is set to 0.001% by weight. However, in order to improve the strength by adding P, it is common to contain 0.04% by weight or more of P.
【０００６】しかし、Ｓｉ及びＭｎは、熱間圧延時にス
ケール内層で内部酸化され、スケールと下地鋼との界面
に酸化物として濃縮する性質をもっている。生成したＳ
ｉ系及びＭｎ系の酸化物や鋼中に分散しているセメンタ
イト（Ｆｅ3 Ｃ）等は、塩酸，硫酸等を使用した脱スケ
ール酸洗で完全に除去することが難しく、酸洗後も鋼板
表面にスマットとして残存する。スマットは、Ｓｉ系酸
化物，Ｍｎ系酸化物，セメンタイト等からなり、水素−
窒素雰囲気中での還元加熱によっても還元又は分解しな
い。表面にスマットがある鋼板をそのままめっき浴に浸
漬すると、めっき金属に対する鋼板表面の濡れ性がスマ
ットにより著しく劣化する。その結果、不めっき，密着
不良等のめっき欠陥が発生する。However, Si and Mn have the property of being internally oxidized in the inner layer of the scale during hot rolling and being concentrated as an oxide at the interface between the scale and the base steel. Generated S
It is difficult to completely remove i-type and Mn-type oxides and cementite (Fe 3 C) dispersed in steel by descaling pickling using hydrochloric acid, sulfuric acid, etc. It remains as smut on the surface. The smut is made of Si-based oxide, Mn-based oxide, cementite, etc.
It is not reduced or decomposed even by reduction heating in a nitrogen atmosphere. When a steel sheet having a smut on its surface is immersed in a plating bath as it is, the wettability of the steel sheet surface with respect to the plating metal is significantly deteriorated by the smut. As a result, plating defects such as non-plating and poor adhesion occur.
【０００７】本発明においては、脱スケール酸洗した熱
延鋼板の表面に残留しているスマットを、弱酸化処理に
先立って鋼板表面から除去する。脱スマット処理には、
ブラッシング等の機械的手段，電解等の電気化学的手
段，物理的手段等が採用される。脱スマット処理せずに
弱酸化処理すると、スマット残留部分と他の鋼表面の酸
化傾向が異なり、Ｆｅの酸化皮膜が鋼板表面に均一な厚
みで形成されない。具体的には、スマットで覆われてい
る部分では、生成したＦｅの酸化皮膜が薄くなる。脱ス
マット処理された熱延鋼板は、清浄化された表面状態に
なる。この熱延鋼板を弱酸化すると、均一な厚みを持つ
Ｆｅの酸化皮膜が鋼板表面に形成される。予熱炉で弱酸
化するとき、予熱炉の空気比を１．００〜１．２０の範
囲に維持することが好ましい。１．００未満では、燃料
が過剰で、余剰酸素を含まない雰囲気となる。そのた
め、めっき性の改善に最低限必要な膜厚を持つＦｅの酸
化皮膜が生成しない。しかし、１．２０を超える空気比
では、Ｆｅの酸化皮膜が適正厚み以上に成長し、却って
還元不十分に起因した不めっきが発生する。In the present invention, the smut remaining on the surface of the descaled pickled hot rolled steel sheet is removed from the surface of the steel sheet prior to the weak oxidation treatment. For desmutting treatment,
Mechanical means such as brushing, electrochemical means such as electrolysis, physical means and the like are adopted. If the weak oxidization treatment is performed without desmutting treatment, the smut residual portion and the other steel surface have different oxidation tendencies, and the Fe oxide film is not formed on the steel sheet surface with a uniform thickness. Specifically, in the portion covered with the smut, the generated Fe oxide film becomes thin. The desmutted hot-rolled steel sheet has a cleaned surface state. When this hot rolled steel sheet is weakly oxidized, an Fe oxide film having a uniform thickness is formed on the surface of the steel sheet. When weakly oxidizing in the preheating furnace, it is preferable to maintain the air ratio of the preheating furnace in the range of 1.00 to 1.20. When it is less than 1.00, the fuel is excessive and the atmosphere does not contain excess oxygen. Therefore, the Fe oxide film having the minimum film thickness required for improving the plating property is not formed. However, when the air ratio exceeds 1.20, the oxide film of Fe grows to an appropriate thickness or more, and conversely non-plating occurs due to insufficient reduction.
【０００８】弱酸化により生成したＦｅの酸化皮膜は、
後続する還元工程で完全にＦｅに還元されるまで、Ｓｉ
やＭｎが鋼中から表面に拡散することを抑制する作用を
呈する。このとき、Ｆｅの酸化皮膜が均一な厚みで鋼板
表面に形成されているので、拡散抑制作用が最大限発揮
される。したがって、還元炉での加熱中に易酸化性元素
の選択酸化が抑制され、不めっき発生の原因となるＳ
ｉ，Ｍｎの濃縮・偏析がなくなる。弱酸化で形成するＦ
ｅの酸化皮膜は、還元工程で所期の還元処理効果を得る
ため、５００〜１００００Åの膜厚が必要である。膜厚
が５００Å未満では、還元工程の初期段階で酸化皮膜か
ら金属Ｆｅへの還元反応が完了してしまい、引き続き行
われる還元加熱中に鋼中のＳｉやＭｎが表面まで拡散す
る。表面に拡散したＳｉやＭｎは、雰囲気に含まれてい
る微量の水分や酸素によって選択酸化され、めっき性を
阻害する表面濃縮層となる。逆に、１００００Åを超え
る膜厚では、還元不足に起因した不めっきが発生し易く
なる。仮に還元が終了していても、十分なめっき密着性
が得られない。The Fe oxide film formed by weak oxidation is
In the subsequent reduction step, until completely reduced to Fe, Si
And Mn have the effect of suppressing the diffusion of Mn from the surface of the steel. At this time, since the Fe oxide film is formed on the surface of the steel sheet with a uniform thickness, the diffusion suppressing effect is maximized. Therefore, the selective oxidation of the easily oxidizable element is suppressed during heating in the reducing furnace, and S that causes non-plating occurs.
Concentration and segregation of i and Mn are eliminated. F formed by weak oxidation
The oxide film of e requires a film thickness of 500 to 10,000 Å in order to obtain the desired reduction treatment effect in the reduction process. If the film thickness is less than 500Å, the reduction reaction from the oxide film to metallic Fe is completed in the initial stage of the reduction process, and Si and Mn in the steel diffuse to the surface during the subsequent reduction heating. The Si and Mn diffused on the surface are selectively oxidized by a small amount of water and oxygen contained in the atmosphere, and become a surface concentrated layer that hinders the plating property. On the other hand, if the film thickness exceeds 10,000 Å, non-plating due to insufficient reduction tends to occur. Even if the reduction is completed, sufficient plating adhesion cannot be obtained.
【０００９】還元加熱工程では、弱酸化処理によって生
成したＦｅの酸化皮膜を金属Ｆｅまで完全に還元する。
還元加熱された鋼板表面は、活性な還元Ｆｅとなり、溶
融めっき性に優れた表面状態に改質される。還元加熱雰
囲気の還元力は、Ｆｅの酸化皮膜を金属Ｆｅに還元する
還元力以上で、且つ鋼中Ｓｉ，Ｍｎがめっき性を阻害す
る程度にまで表面に濃縮し始める還元力未満に設定され
る。このことから、雰囲気の水素濃度を３〜２５容量％
の範囲に設定することが必要である。水素濃度が３容量
％未満では還元力が弱すぎるため、Ｆｅの酸化皮膜が完
全に還元されずに残留し、残留皮膜が不めっき発生の原
因となる。しかし、２５容量％を超える水素濃度では、
還元力が強すぎることから還元過多になり、鋼中Ｓｉ，
Ｍｎが表面まで拡散し選択酸化される。その結果、Ｓ
ｉ，Ｍｎが酸化物として表面に濃縮し、めっき性が阻害
される。In the reduction heating step, the Fe oxide film formed by the weak oxidation treatment is completely reduced to metallic Fe.
The surface of the steel sheet that has been reduced and heated becomes active reduced Fe and is modified into a surface state having excellent hot dip galvanizing properties. The reducing power of the reducing heating atmosphere is set to be more than the reducing power for reducing the oxide film of Fe to metallic Fe and less than the reducing power for Si and Mn in the steel to start concentrating on the surface to the extent that the plating property is hindered. . From this, the hydrogen concentration in the atmosphere is 3 to 25% by volume.
It is necessary to set within the range. When the hydrogen concentration is less than 3% by volume, the reducing power is too weak, so that the oxide film of Fe remains without being completely reduced, and the residual film causes non-plating. However, at a hydrogen concentration exceeding 25% by volume,
Since the reducing power is too strong, there is excessive reduction, and Si in steel,
Mn diffuses to the surface and is selectively oxidized. As a result, S
i and Mn are concentrated on the surface as oxides, and the plating property is hindered.
【００１０】還元加熱雰囲気の水素濃度が酸化皮膜の還
元に与える影響を、図１を参照しながら具体的に説明す
る。図１で使用した試験片は、１．２重量％のＳｉを含
む高張力熱延鋼板を脱スケール酸洗した後、ブラッシン
グでスマットを除去し、弱酸化処理で１０００Åの膜厚
を持つＦｅの酸化皮膜を形成したものを使用した。水素
濃度がそれぞれ１容量％，１５容量％及び５０容量％の
Ｈ2 −Ｎ2 還元性雰囲気で試験片を還元加熱し、還元加
熱後の試験片をオージェ電子分光分析した。図１（ｂ）
から明らかなように、水素濃度１５容量％の雰囲気で還
元加熱したとき、試験片の表面は、Ｓｉ及びＭｎの濃縮
が検出されず、実質的に還元Ｆｅのみであった。他方、
水素濃度１容量％の雰囲気で還元加熱した試験片では、
図１（ａ）に示すように、表層にＦｅの酸化皮膜が残存
していた。逆に、水素濃度５０容量％の雰囲気で還元加
熱した試験片では、図１（ｃ）に示すように、試験片表
面におけるＳｉ，Ｏの顕著な濃化が検出された。The effect of the hydrogen concentration in the reducing heating atmosphere on the reduction of the oxide film will be specifically described with reference to FIG. The test piece used in Fig. 1 was prepared by descaling a high-strength hot-rolled steel sheet containing 1.2% by weight of Si, removing smut by brushing, and performing weak oxidation treatment to remove Fe with a thickness of 1000 Å. What formed the oxide film was used. The test pieces were subjected to reduction heating in a H 2 —N 2 reducing atmosphere having hydrogen concentrations of 1% by volume, 15% by volume and 50% by volume, respectively, and the test pieces after the reduction heating were subjected to Auger electron spectroscopy analysis. Figure 1 (b)
As is clear from the above, when reduced and heated in an atmosphere having a hydrogen concentration of 15% by volume, Si and Mn concentration was not detected on the surface of the test piece, and substantially only reduced Fe was found. On the other hand,
In the test piece which was reduced and heated in the atmosphere of hydrogen concentration of 1% by volume
As shown in FIG. 1A, an oxide film of Fe remained on the surface layer. On the contrary, in the test piece which was reduced and heated in the atmosphere having a hydrogen concentration of 50% by volume, as shown in FIG. 1C, a remarkable concentration of Si and O was detected on the surface of the test piece.
【００１１】[0011]
【作用】本発明においては、脱スケール酸洗後に脱スマ
ット処理した熱延鋼板の表面に５００〜１００００Åの
膜厚をもつＦｅの酸化皮膜を均一に形成した後、水素濃
度３〜２５容量％の雰囲気中で還元加熱することによ
り、鋼中Ｓｉ，Ｍｎを表面濃縮させることなく、Ｆｅの
酸化皮膜を完全に金属Ｆｅまで還元している。これによ
り、熱延鋼板の表面が活性な還元Ｆｅになり、不めっき
等の欠陥を発生することがない溶融めっき性に優れた表
面状態が得られる。In the present invention, an oxide film of Fe having a film thickness of 500 to 10000Å is uniformly formed on the surface of a hot rolled steel sheet desmutted after descaling and pickling, and then hydrogen concentration of 3 to 25% by volume is applied. By reducing and heating in an atmosphere, the oxide film of Fe is completely reduced to metallic Fe without surface-concentrating Si and Mn in steel. As a result, the surface of the hot-rolled steel sheet becomes active reduced Fe, and a surface state excellent in hot-dip galvanizing property without causing defects such as non-plating can be obtained.
【００１２】[0012]
【実施例】 実施例１：めっき原板として、表１に示した組成を持つ
４種の高張力熱延鋼板を使用した。各熱延鋼板を連続式
溶融めっきラインで塩酸脱スケール酸洗した後、ブラシ
ロール又は陽極電解によって脱スマット処理した。陽極
電解は、キレート剤を含む強アルカリ脱脂液５０ｇ／ｌ
及びＮａＯＨ５０ｇ／ｌの浴を使用し、浴温４０℃，電
流密度１５Ａ／ｄｍ2 ，電解時間１０秒の電解条件を採
用した。[Examples] Example 1: Four types of high-strength hot-rolled steel sheets having the compositions shown in Table 1 were used as plating base sheets. Each hot rolled steel sheet was subjected to descaling with hydrochloric acid in a continuous hot dip coating line, and then desmutted by brush rolls or anodic electrolysis. Anodic electrolysis is a strong alkaline degreasing solution containing a chelating agent 50g / l
And a NaOH 50 g / l bath were used, and electrolysis conditions of a bath temperature of 40 ° C., a current density of 15 A / dm 2 , and an electrolysis time of 10 seconds were adopted.
【００１３】[0013]
【表１】 [Table 1]
【００１４】脱スマット処理された各熱延鋼板を、直ち
に予熱炉に装入し、空気比０．９０〜１．２０の弱酸化
性雰囲気中で弱酸化処理した。弱酸化処理で生成される
Ｆｅの酸化皮膜は、空気比及び鋼板温度によって膜厚が
決まってくる。そこで、適正な膜厚を持つＦｅの酸化皮
膜が形成されるように、予熱炉の空気比及び板温を管理
した。Ｆｅの酸化皮膜が形成された熱延鋼板は、何れも
水素濃度１０容量％の還元性雰囲気が維持された還元炉
で還元加熱した後、大気に曝されることなく溶融Ｚｎめ
っきした。還元炉は最大加熱能力の７０〜８０％で操業
し、加熱能力，板厚，板幅等に応じて通板速度を選定し
た。具体的には、板厚３．２ｍｍ及び板幅１０００ｍｍ
の熱延鋼板を通板速度３２ｍ／分で通板し、還元炉の滞
在時間を３０秒に設定した。めっき浴には、Ｚｎ−０．
１４％Ａｌ合金を使用した。製造されためっき鋼板の外
観を観察し、めっき欠陥がないものを○，不めっきが発
生したものを×，ピンホール状の不めっきが発生したも
のを△として評価した。また、めっき外観が良好な鋼板
から試験片を切り出し、めっき密着性試験に供した。密
着性試験は、試験片を１８０度曲げ、屈曲部の外側に粘
着テープを貼り付け、引き剥した後、粘着テープに転写
されためっき層の有無により判定した。粘着テープにめ
っき層が転写されないものを○として評価した。Each desmutted hot-rolled steel sheet was immediately charged into a preheating furnace and subjected to a weak oxidation treatment in a weak oxidizing atmosphere with an air ratio of 0.90 to 1.20. The film thickness of the Fe oxide film formed by the weak oxidation treatment is determined by the air ratio and the steel plate temperature. Therefore, the air ratio and plate temperature of the preheating furnace were controlled so that an Fe oxide film having an appropriate film thickness was formed. Each of the hot-rolled steel sheets on which the Fe oxide film was formed was subjected to reduction heating in a reducing furnace in which a reducing atmosphere having a hydrogen concentration of 10% by volume was maintained, and then hot-dip Zn plating without being exposed to the atmosphere. The reduction furnace was operated at 70 to 80% of the maximum heating capacity, and the plate passing speed was selected according to the heating capacity, plate thickness, plate width, etc. Specifically, a plate thickness of 3.2 mm and a plate width of 1000 mm
The hot-rolled steel sheet of No. 1 was passed at a stripping speed of 32 m / min, and the residence time in the reduction furnace was set to 30 seconds. The plating bath contains Zn-0.
A 14% Al alloy was used. The appearance of the manufactured plated steel sheet was observed, and those having no plating defects were evaluated as ◯, those in which non-plating occurred were evaluated as x, and those in which pinhole-shaped non-plating occurred were evaluated as Δ. Further, a test piece was cut out from a steel plate having a good plating appearance and subjected to a plating adhesion test. In the adhesion test, the test piece was bent 180 degrees, an adhesive tape was attached to the outside of the bent portion, peeled off, and then judged by the presence or absence of the plating layer transferred to the adhesive tape. The case where the plating layer was not transferred to the adhesive tape was evaluated as ◯.
【００１５】[0015]
【表２】 [Table 2]
【００１６】評価結果を製造条件と共に示す表２から明
らかなように、本発明に従った脱スマット処理，弱酸化
処理及び還元加熱が施された熱延鋼板を溶融めっきする
と、何れもめっき外観及びめっき密着性の双方に優れて
いることが判る。これは、５００〜１００００Åの膜厚
をもつＦｅの酸化皮膜が鋼板表面に均一に形成され、こ
の酸化皮膜が還元加熱で金属Ｆｅまで還元されることに
よって、活性表面をもつ熱延鋼板がめっき浴に導入され
たことを示す。これに対し、Ｆｅの酸化皮膜が薄すぎる
比較例１，５，１１，１６及び１９では、不めっきが発
生していた。予熱工程において空気比１．０未満の雰囲
気で酸化した比較例８〜１０も、生成したＦｅの酸化皮
膜が薄く、同様に不めっきが発生していた。また、脱ス
マット処理を施さなかった比較例２２〜２５では、不め
っき，ピンホール等が観察された表面層を呈していた。
これは、予熱工程で、不均一なＦｅの酸化皮膜が生成し
たことに起因するものと推察される。As is clear from Table 2 which shows the evaluation results together with the production conditions, when hot-rolled steel sheets subjected to desmutting treatment, weak oxidation treatment and reduction heating according to the present invention were hot-dipped, the plating appearance and It can be seen that the plating adhesion is excellent. This is because an oxide film of Fe having a film thickness of 500 to 10000Å is uniformly formed on the surface of the steel sheet, and this oxide film is reduced to metallic Fe by reduction heating, so that the hot-rolled steel sheet having an active surface forms a plating bath. It was introduced in. On the other hand, in Comparative Examples 1, 5, 11, 16 and 19 in which the Fe oxide film was too thin, non-plating occurred. Also in Comparative Examples 8 to 10 that were oxidized in an atmosphere with an air ratio of less than 1.0 in the preheating step, the produced Fe oxide film was thin and similarly non-plating occurred. Further, in Comparative Examples 22 to 25 which were not subjected to desmutting treatment, the surface layer in which non-plating, pinholes, etc. were observed was exhibited.
It is speculated that this is due to the formation of a non-uniform Fe oxide film in the preheating step.
【００１７】実施例２：鋼種Ａ及びＤの熱延鋼板をめっ
き原板として使用し、脱スケール酸洗及び脱スマット処
理した後、直ちに空気比１．０５〜１．２０の予熱炉で
加熱することにより所定膜厚を持つＦｅの酸化皮膜を形
成した。次いで、水素濃度１〜４０容量％の還元性雰囲
気に維持した還元炉で熱延鋼板を還元加熱し、大気に曝
されることなく実施例１と同じめっき浴で溶融めっきし
た。なお、実施例２では、何れもブラッシングによる脱
スマット処理を採用した。また、還元炉の操業条件及び
通板条件は、実施例１と同様に設定した。得られためっ
き鋼板のめっき性を、製造条件と併せて表３に示す。表
３から明らかなように、本発明に従うとき、めっき外観
及びめっき密着性共に優れた溶融亜鉛めっき高張力鋼板
が製造されることが判る。他方、予熱工程までを同様に
処理されたものであっても、水素濃度が３〜２５容量％
の範囲を外れる水素濃度の雰囲気で還元加熱した比較例
では、何れもめっき外観が劣っていた。Example 2: Using hot-rolled steel sheets of steel types A and D as a plating original plate, after descaling pickling and desmutting treatment, immediately heating in a preheating furnace with an air ratio of 1.05 to 1.20 To form an oxide film of Fe having a predetermined film thickness. Then, the hot-rolled steel sheet was reduction-heated in a reducing furnace maintained in a reducing atmosphere having a hydrogen concentration of 1 to 40% by volume, and hot-dipped in the same plating bath as in Example 1 without being exposed to the atmosphere. In addition, in Example 2, desmutting treatment by brushing was adopted in all cases. Further, the operating conditions and strip passing conditions of the reduction furnace were set in the same manner as in Example 1. The plating properties of the obtained plated steel sheet are shown in Table 3 together with the production conditions. As is clear from Table 3, when the present invention is used, hot-dip galvanized high-strength steel sheets having excellent plating appearance and plating adhesion are manufactured. On the other hand, even if the pre-heating process is the same, the hydrogen concentration is 3 to 25% by volume.
In each of the comparative examples heated by reduction in an atmosphere having a hydrogen concentration outside the range, the plating appearance was inferior.
【００１８】[0018]
【表３】 [Table 3]
【００１９】実施例３：鋼種Ａ及びＤの熱延鋼板を脱ス
ケール酸洗した後、何れもブラシロールで脱スマット処
理し、直ちに空気比１．００〜１．２０の予熱炉で加熱
した。所定の膜厚を持つＦｅの酸化皮膜が形成された熱
延鋼板は、何れも水素濃度２０容量％の還元炉で還元加
熱された後、大気に曝されることなく溶融めっき浴に導
入された。還元炉の操業条件及び通板条件は、実施例１
と同様に設定した。また、溶融めっき浴には、Ｚｎ−４
％Ａｌ，Ｚｎ−５５％Ａｌ及びＡｌ−９％Ｓｉの３種を
使用した。得られためっき鋼板のめっき性を、製造条件
と併せて表４に示す。表４から明らかなように、本発明
に従うとき、Ｚｎ−Ａｌめっき鋼板及びＡｌめっき鋼板
の何れも外観及び密着性に優れた溶融めっき層が形成さ
れていることが判る。しかし、同様に処理されたもので
も、予熱工程で膜厚が１００００Åを超えるＦｅの酸化
皮膜が形成されたものでは、何れもめっき外観が劣って
いた。Example 3 After hot-rolled steel sheets of steel types A and D were descaled and pickled, they were desmutted with a brush roll and immediately heated in a preheating furnace with an air ratio of 1.00 to 1.20. Each of the hot-rolled steel sheets on which an Fe oxide film having a predetermined film thickness was formed was reduced and heated in a reducing furnace having a hydrogen concentration of 20% by volume, and then introduced into a hot dip bath without being exposed to the atmosphere. . The operating conditions and strip running conditions of the reduction furnace are as shown in Example 1.
The same setting was made. Further, in the hot dip plating bath, Zn-4
% Al, Zn-55% Al and Al-9% Si were used. The plateability of the obtained plated steel sheet is shown in Table 4 together with the production conditions. As is apparent from Table 4, when the present invention is followed, it is understood that the hot dip plated layer having excellent appearance and adhesion is formed on both the Zn-Al plated steel sheet and the Al plated steel sheet. However, even in the case of the same treatment, the appearance of plating was inferior in all cases in which the oxide film of Fe having a film thickness of over 10000Å was formed in the preheating step.
【００２０】[0020]
【表４】 [Table 4]
【００２１】[0021]
【発明の効果】以上に説明したように、本発明において
は、脱スケール酸洗された熱延鋼板表面に残留している
スマットを除去し、清浄な表面状態にして弱酸化及び還
元加熱を施している。そのため、弱酸化によって鋼板表
面に均一な厚みをもつＦｅの酸化皮膜が形成され、還元
加熱時に鋼中のＳｉ及びＭｎが選択酸化されて表面に濃
縮することが抑制される。還元加熱された鋼板表面は、
めっき金属に対して濡れ性の良好な活性な還元Ｆｅにな
っている。このようにして本発明によるとき、従来難め
っき材とされてきた高張力熱延鋼板の溶融めっき性が改
善され、連続めっきラインで溶融Ｚｎ，溶融Ｚｎ−Ａ
ｌ，溶融Ａｌ等の各種めっき鋼板を製造することが可能
になる。得られためっき鋼板は、外観及び密着性に優れ
ためっき層をもち、構造材，建材，部品等として広範な
分野で使用される。As described above, in the present invention, the smut remaining on the surface of the hot-rolled steel sheet that has been descaled and pickled is removed to obtain a clean surface state, and a weak oxidation and reduction heating are performed. ing. Therefore, an oxide film of Fe having a uniform thickness is formed on the surface of the steel sheet by weak oxidation, and Si and Mn in the steel are suppressed from being selectively oxidized and concentrated on the surface during reduction heating. The reduction-heated steel plate surface is
It is an active reduced Fe that has good wettability with respect to the plating metal. As described above, according to the present invention, the hot dip galvanizing property of the high-strength hot-rolled steel sheet, which has been conventionally regarded as a hard-to-dip material, is improved, and the hot-dip Zn, hot-dip Zn-A in the continuous plating line
It becomes possible to manufacture various plated steel sheets such as 1 and molten Al. The obtained plated steel sheet has a plated layer excellent in appearance and adhesion, and is used in a wide range of fields as a structural material, a building material, parts and the like.
【図１】 適正な膜厚を持つＦｅの酸化皮膜を形成した
鋼板表面を還元加熱したとき、オージェ電子分光分析に
よる表面からの深さ方向分析結果に還元性雰囲気の水素
濃度が及ぼした影響を示すグラフFIG. 1 shows the influence of the hydrogen concentration in a reducing atmosphere on the depth direction analysis result from the surface by Auger electron spectroscopy when the surface of a steel sheet on which an Fe oxide film having an appropriate film thickness is formed is reduced and heated. Graph showing
Claims (1)
力熱延鋼板を脱スケール酸洗後に脱スマット処理し、弱
酸化性雰囲気中で加熱して鋼板表面に５００〜１０００
０Åの膜厚を持つＦｅの酸化皮膜を形成した後、水素濃
度３〜２５容量％の雰囲気に保持された還元炉で還元加
熱し、次いで溶融めっきすることを特徴とする高張力熱
延鋼板の溶融めっき方法。1. A high-strength hot-rolled steel sheet containing Si and Mn as strengthening elements is subjected to descaling pickling, desmutting treatment, and heating in a weakly oxidizing atmosphere to heat the steel sheet surface to 500 to 1000.
After forming an Fe oxide film having a film thickness of 0Å, reduction heating is performed in a reducing furnace kept in an atmosphere having a hydrogen concentration of 3 to 25% by volume, and then hot dip plating is performed. Hot dipping method.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP00656494A JP3277063B2 (en) | 1994-01-25 | 1994-01-25 | Hot-dip galvanizing method for high-strength hot-rolled steel sheet |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP00656494A JP3277063B2 (en) | 1994-01-25 | 1994-01-25 | Hot-dip galvanizing method for high-strength hot-rolled steel sheet |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH07216524A true JPH07216524A (en) | 1995-08-15 |
| JP3277063B2 JP3277063B2 (en) | 2002-04-22 |
Family
ID=11641838
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP00656494A Expired - Lifetime JP3277063B2 (en) | 1994-01-25 | 1994-01-25 | Hot-dip galvanizing method for high-strength hot-rolled steel sheet |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3277063B2 (en) |
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| WO1998030729A1 (en) * | 1997-01-13 | 1998-07-16 | Kawasaki Steel Corporation | Hot dip galvanized steel sheet reduced in defects derived from failed plating and excellent in contact plating adhesion and process for producing the same |
| FR2824079A1 (en) * | 2001-04-25 | 2002-10-31 | Kobe Steel Ltd | HOT-DIP GALVANIZED STEEL SHEET |
| KR100368728B1 (en) * | 1998-12-29 | 2003-03-31 | 주식회사 포스코 | Manufacturing method of hot-dip galvanized steel sheet containing silicon |
| DE102006039307B3 (en) * | 2006-08-22 | 2008-02-21 | Thyssenkrupp Steel Ag | Process for coating a 6-30 wt.% Mn-containing hot or cold rolled steel strip with a metallic protective layer |
| DE102008005605A1 (en) | 2008-01-22 | 2009-07-23 | Thyssenkrupp Steel Ag | Process for coating a 6-30% by weight Mn-containing hot or cold rolled flat steel product with a metallic protective layer |
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| WO2012070694A1 (en) * | 2010-11-26 | 2012-05-31 | Ｊｆｅスチール株式会社 | Al-Zn-BASED HOT-DIP PLATED STEEL SHEET AND MANUFACTURING METHOD THEREOF |
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| US9034480B2 (en) | 2010-11-26 | 2015-05-19 | Jfe Steel Corporation | Hot-dip Al—Zn coated steel sheet |
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| WO1998030729A1 (en) * | 1997-01-13 | 1998-07-16 | Kawasaki Steel Corporation | Hot dip galvanized steel sheet reduced in defects derived from failed plating and excellent in contact plating adhesion and process for producing the same |
| EP0900857A1 (en) * | 1997-01-13 | 1999-03-10 | Kawasaki Steel Corporation | Hot dip galvanized steel sheet reduced in defects derived from failed plating and excellent in contact plating adhesion and process for producing the same |
| EP0900857A4 (en) * | 1997-01-13 | 2000-08-02 | Kawasaki Steel Co | Hot dip galvanized steel sheet reduced in defects derived from failed plating and excellent in contact plating adhesion and process for producing the same |
| KR100325755B1 (en) * | 1997-01-13 | 2002-07-18 | 에모토 간지 | Zinc-zinc-alloy hot-dip galvanized steel sheet with low unplated defects and excellent coating adhesion and manufacturing method thereof |
| KR100368728B1 (en) * | 1998-12-29 | 2003-03-31 | 주식회사 포스코 | Manufacturing method of hot-dip galvanized steel sheet containing silicon |
| FR2824079A1 (en) * | 2001-04-25 | 2002-10-31 | Kobe Steel Ltd | HOT-DIP GALVANIZED STEEL SHEET |
| DE102006039307B3 (en) * | 2006-08-22 | 2008-02-21 | Thyssenkrupp Steel Ag | Process for coating a 6-30 wt.% Mn-containing hot or cold rolled steel strip with a metallic protective layer |
| US8394213B2 (en) | 2006-08-22 | 2013-03-12 | Thyssenkrupp Steel Ag | Process for coating a hot- or cold- rolled steel strip containing 6−30% by weight of MN with a metallic protective layer |
| WO2009092733A2 (en) | 2008-01-22 | 2009-07-30 | Thyssenkrupp Steel Ag | Method for coating a warm or cold-rolled flat steel product comprising 6 – 30 weight-% mn with a metallic protective layer |
| DE102008005605A1 (en) | 2008-01-22 | 2009-07-23 | Thyssenkrupp Steel Ag | Process for coating a 6-30% by weight Mn-containing hot or cold rolled flat steel product with a metallic protective layer |
| US8506731B2 (en) | 2008-01-22 | 2013-08-13 | Thyssenkrupp Steel Europe Ag | Method for coating a hot-rolled or cold-rolled steel flat product containing 6-30 wt% Mn |
| JP2010150660A (en) * | 2008-12-23 | 2010-07-08 | Posco | Method for producing hot dip galvanized steel sheet of high manganese steel having excellent plating surface quality |
| US20140144550A1 (en) * | 2010-08-31 | 2014-05-29 | Thyssenkrupp Steel Europe Ag | Method for Hot Dip Coating of a Flat Steel Product |
| US9279175B2 (en) * | 2010-08-31 | 2016-03-08 | Thyssenkrupp Steel Europe Ag | Method for hot dip coating a flat steel product |
| WO2012070694A1 (en) * | 2010-11-26 | 2012-05-31 | Ｊｆｅスチール株式会社 | Al-Zn-BASED HOT-DIP PLATED STEEL SHEET AND MANUFACTURING METHOD THEREOF |
| KR20130112052A (en) * | 2010-11-26 | 2013-10-11 | 제이에프이 스틸 가부시키가이샤 | Al-zn-based hot-dip plated steel sheet and manufacturing method thereof |
| US9034480B2 (en) | 2010-11-26 | 2015-05-19 | Jfe Steel Corporation | Hot-dip Al—Zn coated steel sheet |
| US9234267B2 (en) | 2010-11-26 | 2016-01-12 | Jfe Steel Corporation | Hot-dip Al—Zn coated steel sheet |
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